A fixing device is known that includes an endless belt, a heating element and a nip member that are disposed in the endless belt, a backup member that nips the endless belt together with the nip member so as to form a nip together with the endless belt, and a reflection member that reflects radiant heat from the heating element towards the nip member (see JP2011095534A). Specifically, in the above technique, the reflection member is configured in a U-shape in cross-sectional view and is in contact with both edge portions of the nip member in the sheet transport direction from the opposite side with respect to the backup member. Furthermore, portions of the reflection member that are in contact with the nip member are formed so as to extend across substantially one end to substantially the other end of the nip member in the longitudinal direction (in detail, an area corresponding to one end to the other end of the nip).